X0306 4 2021-12-10 0 0001666134 BLACKLINE, INC. BL 0001688366 Partin Mark 21300 VICTORY BLVD 12TH FLOOR WOODLAND HILLS CA 91367 0 1 0 0 Chief Financial Officer Common Stock 2021-12-10 4 M 0 5000 14.00 A 95715 D Common Stock 2021-12-10 4 S 0 3297 105.4747 D 92418 D Common Stock 2021-12-10 4 S 0 1003 106.1656 D 91415 D Common Stock 2021-12-10 4 S 0 700 107.1479 D 90715 D Stock Option (right to buy) 14.00 2021-12-10 4 M 0 5000 0.00 D 2025-03-29 Common Stock 5000 137676 D The sale transaction reported on this Form 4 was effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on March 12, 2021. The sale price represents the weighted-average price of shares sold ranging from $104.80 to $105.79 per share. Upon request by the Securities and Exchange Commission staff, the Issuer or a security holder of the Issuer, the Reporting Person will provide full information regarding the number of shares sold at each separate price within the range set forth in this Form 4. The sale price represents the weighted-average price of shares sold ranging from $105.92 to $106.67 per share. Upon request by the Securities and Exchange Commission staff, the Issuer or a security holder of the Issuer, the Reporting Person will provide full information regarding the number of shares sold at each separate price within the range set forth in this Form 4. The sale price represents the weighted-average price of shares sold ranging from $106.83 to $107.43 per share. Upon request by the Securities and Exchange Commission staff, the Issuer or a security holder of the Issuer, the Reporting Person will provide full information regarding the number of shares sold at each separate price within the range set forth in this Form 4. The shares subject to the option vest in 4 equal, annual installments beginning on the one year anniversary of January 20, 2015. /s/ Karole Morgan-Prager, Attorney-in-Fact 2021-12-10